The present invention relates to a new and improved construction of a rotational or rotary bearing arrangement for high speeds of rotation and to a method of fabrication of such rotational or rotary bearing arrangement.
Generally speaking, the rotational or rotary bearing arrangement for high speeds of rotation comprises a casing or housing and a shaft which is rotatably mounted therein. The shaft has a first track and a second track for receiving the respective balls of a first ball bearing and a second ball bearing. A closed first ball cage is associated with the first ball bearing and a closed second ball cage is associated with the second ball bearing. A first outer race is associated with the first ball bearing and a second outer race is associated with the second ball bearing. The outer races are disposed in a respective first hollow substantially cylindrical seat and a second hollow cylindrical seat, which seats are coaxially arranged with respect to the rotational axis of the rotational bearing arrangement and are formed by the casing or housing.
Rotational bearing arrangements of this type are known, for example, from German Pat. No. 2,113,905, published Oct. 14, 1971 and from Swiss Pat. No. 514,796, granted Oct. 31, 1971. They are widely used to drive spinning centrifuges of open-end spinning machines where there occur speeds of up to 100,000 revolutions per minute.
It is therefore desirable for the peripheral or circumferential speed of the balls of the ball bearings to be as small as possible. Hence, the shaft itself is formed with tracks operative or effective as ball bearing inner races, the balls running in such tracks. This greatly reduces the distance which the balls have to travel per revolution.
It has been found that these known arrangements or systems may be subject to vibrations and excessive wear which reduce their service or working life in an unsatisfactory manner. These disadvantages occur when the required high precision of the components is unsatisfactory. More particularly, the distance between the ball tracks on the shaft and the distance between the bearing outer races must be adapted to one another very accurately. The length of the spacer sleeves or bushings which are used in these known arrangements or systems and with which the outer races are in engagement must therefore be very accurate, but it is difficult in practice to achieve the required accuracy.
According to German Published Patent Application No. 3,605,274 A1, published Sept. 11, 1987, to enable the rotational bearing arrangement to run at very high speeds, the shaft is constructed in two parts which are introduced into a bushing or sleeve and thus held together. The required between-tracks spacing can be adjusted by varying the axial distance between the two parts of the shaft. However, in this construction the fact that the two relatively heavy shaft parts are clamped in the bushing impairs the linearity or straightness of the shaft, leading to difficulties at the very high speeds of rotation which occur. The necessary accurate adjustability cannot be provided and difficulties occur because of balancing problems.